In the past, a substrate has been coated with a solution of an organic compound containing metal elements of which a superconductive material is formed to be subsequently dried (1), and thereafter, a process step (2) (provisional baking) for executing decomposition of organic components, and a process step (3) (main baking) for forming the superconductive material have all been executed by the agency of thermal energy (refer to Patent Document 1).
Further, there has been known a method of producing metal oxides, and metal oxide thin films by use of an excimer laser (refer to Patent Document 2), characterized in that when preparing metal oxides (exhibiting no superconductivity), metal salts of organic acids, or metalorganic compounds MmRn (provided that M=Si, Ge, Sn, Pb among the group 4b elements, Cr, Mo, W among the group 6a elements, and Mn, Tc, Re among the group 7a elements; R=an alkyl group such as CH3, C2H5, C3H7, C4H5, etc., a carboxyl group such as CH3COO−, C2H5COO−, C3H7COO−, C4H9COO−, etc., or a carbonyl group of CO; m, n: integers) are dissolved in a soluble solvent (or if those are in liquid form, as they are), and a solution thus obtained is dispersed and applied over a substrate before the substrate is irradiated in an oxygen atmosphere with an excimer laser light.
Still further, there has been known a method of producing metal oxides, which is a method of producing metal oxides (exhibiting no superconductivity) on a substrate without applying heat treatment at a high temperature unlike a conventional case known as the coating thermal decomposition method, characterized in that metalorganic compounds (metal salts of organic acids, metal-acetylacetonate, metal-alkoxides containing an organic group having 6 or more carbon atoms) are dissolved in a solvent to be turned into a solution, and the substrate is coated with the solution to be subsequently dried, thereby forming metal oxides on the substrate by irradiating the substrate with laser light at a wavelength not more than 400 nm (Patent Document 3).
Herein, there has been described the method of producing metal oxides, characterized in that the metalorganic compounds are dissolved in the solvent to be turned into the solution, and the substrate is coated with the solution to be subsequently dried, thereby forming metal oxides on the substrate by irradiating the substrate with the laser light at a wavelength not more than 400 nm such as, for example, an excimer laser beam selected from the group consisting of excimer laser beams ArF, KrF, XeCl, XeF and F2, and further, it has been described therein that irradiation with the laser light at the wavelength not more than 400 nm is executed in a plurality of stages, and weaker irradiation on the order not to cause complete decomposition of the metalorganic compounds is executed in the initial stage of the irradiation while executing stronger irradiation capable of converting the metalorganic compounds into the metal oxides in the next stage. Further, it is also known that the metalorganic compounds are not less than two kinds of compounds, each containing a different metal, the metal oxides obtained are composite oxides containing various metals, and respective metal constituents of the metal salts of the organic acids are elements selected from the group consisting of iron, indium, tin, zirconium, cobalt, nickel, and lead.
Still further, with a method of producing composite oxide films, whereby a precursor coating liquid containing raw material constituents of respective oxides of La, Mn and any of Ca, Sr and Ba is applied to a surface of a material to be coated to thereby form a film, and subsequently, a thin film formed on the surface of the material to be coated is caused to undergo crystallization to thereby form composite oxide films (exhibiting no superconductivity) having the perovskite structure expressed by a composition formula (La1-xMx)MnO3-δ (M: Ca, Sr, Ba, 0.09≦x≦0.50), there has been known a method of producing composite oxide films (refer to Patent Document 4) characterized in that the precursor coating liquid is applied to the surface of the material to be coated to thereby form a film, and subsequently, a thin film formed on the surface of the oxide to be coated is irradiated with light at a wavelength not more than 360 nm to thereby crystallize the thin film.
Herein, it is further described that as a light source for irradiating the thin film formed on the surface of the material to be coated with light, use is made of a third harmonic light of ArF excimer laser, KrF excimer laser, XeCl excimer laser, XeF excimer laser, and YAG laser, or a fourth harmonic light of the YAG laser, and the precursor coating liquid to be applied to the surface of the material to be coated is prepared by mixing and reaction of an alkanolamine coordination compound of La, Mn carboxylate, and metal M or M alkoxide together in a first alcohol having carbon atoms in a range of 1 to 4.
The inventors have been faced with the fact that with the conventional method of producing a superconductive material, a long time was required, the orientation was difficult to control, and further, uniformity underwent deterioration due to the occurrence of a reaction with a support body in practical use when carrying out the thermal decomposition of metalorganic compounds, and formation of a superconductive material by means of heat treatment, and in order to overcome these problems, the inventor has succeeded in finding out a method of efficiently producing a superconductive material having an excellent performance upon execution of the thermal decomposition of the metalorganic compounds and the formation of the superconductive material by means of the heat treatment, and has already submitted a Japanese Patent Application (refer to Patent Document 5).
More specifically, such a method is a method of producing a superconductive material, characterized in that laser light is irradiated between the step of applying a solution of an organic compound containing metals, oxides of the metals forming a superconductive material, onto a support body to be subsequently dried (1), and the provisional baking step of causing organic components of the organic compound containing the metals to undergo thermal decomposition (2).
The superconductive material obtained by the method according to this invention is superior in production efficiency, suitable for mass production, and has an excellent superconductivity, however, in the case of a YBa2Cu3O7 (YBCO) film about 100 nm in film thickness, the upper limit of the critical current density has been found on the order of Jc=2.0 MA/cm2 at most. Furthermore, with this invention, only a surface of a substrate, coated with the solution of the organic compound containing the metals for forming the superconductive material on the substrate is simply irradiated with laser light.    Patent Document 1: JP 07-106905-B    Patent Document 2: JP 2759125-W, Specification    Patent Document 3: JP 2001-31417-A    Patent Document 4: JP 2000-256862-A    Patent Document 5: JP application 2006-185934